The present invention relates to a method for manufacturing a sweeper or abrasive element for use in a rotating sweeper, abrasive or polishing tool and comprising bristles or lamellae of abrasive cloth and rigidifying bristles, which are retained in a substantially U-shaped profile.
The invention has originated in the context of manufacturing rotating abrasive and polishing tools. However, the invention may also advantageously be used in the context of sweeper tools such as known, e.g. from brushes mounted on tractors or from other rotating brushes where the sweeper brushes are generally embedded for squeezing in a metal U profile. As the invention primarily originates from the context of abrasive or polishing tools, the following explanation will mainly be based on the disadvantages associated with such tools and, likewise, the advantages of the invention will also primarily be explained in the context of such tools.
Rotating abrasive or polishing tools provided with abrasive elements are known. Such tools are used extensively in the woodworking industry.
Abrasive elements of the type comprising abrasive cloth and rigidifying bristles have obtained widespread use as they give a good result when grinding profiled wooden items.
Abrasive or polishing tools of the type in which the abrasive element is used have so far primarily been used for grinding and polishing non-plane surfaces such as curved furniture parts, panelled doors, etc. The lamellae of the abrasive element are formed by cutting an abrasive cloth transversely of its longitudinal direction so that strips or lamellae appear, which are at one end interconnected by means of an unbroken tape secured to the U profile. The abrasive or polishing effect is obtained as a result of the effect of the lamellae as they sweep over the item during rotation of the tool. The rigidifying brushes, as indicated by the word, have a function of supporting the abrasive lamellae. However, the brushes may also be produced from such a material that they contribute to the abrasive or polishing effect.
A known tool of this type is designated "Flatter polisher". Abrasive or polishing tools of this type are disclosed, e.g. in Danish patent applications No. 191/91 and No. 849/92. These applications also disclose abrasive elements of the type mentioned in the introduction.
Such tools are formed by a number of circular or helical abrasive elements arranged in parallel. The abrasive elements are arranged in a track in a cylinder shell so that a cylindrical abrasive or polishing tool is formed, which has an abrasive or polishing effect from its cylindrical circumference.
The abrasive or polishing effect of the tools appears as a result of the effect of the lamellae during the flexible sweeping of the item during rotation of the tool. During rotation of the tool, merely the centrifugal force will contribute to the abrasive or polishing pressure necessary for the treatment. Furthermore, the rigidity of the lamellae themselves will be important in order to produce the necessary abrasive or polishing pressure. Furthermore, the supporting brushes inserted next to the lamellae will also serve to increase the abrasive pressure of the lamellae, and the brushes may be produced from a material contributing to the abrasive or polishing process.
Polishing, i.e. grinding and inter-paint polishing of wood, is performed in order to obtain the best possible surface quality. Polishing items that are profiled, or which have a complex shape, make heavy requirements on the polishing technique used. The polishing tools and their polishing or abrasive elements must necessarily be very flexible and must be able to adapt to items to be polished in order to ensure a uniform treatment of the surface. Thus, there must be no grinding of edges, and it also has to be ensured that polishing or grinding is established in grooves and adjacent projections.
In these known abrasive elements, the lamellae and the brushes are placed in a U-shaped metal profile, which is subsequently squeezed together around the abrasive lamellae and the brushes. Squeezing of the U profile is performed in such a manner that brushes and lamellae are retained mechanically in the profile. Retention might be improved by means of a metal wire or plastic wire inserted in the U bottom. Said wire increases the cross-section area under the squeezed sides of the U profile. This improves retention as the brushes and possibly also part of the lamellae are folded around the wire. In squeezing the U profile, it is simultaneously given a cross-section shape fitting into undercut tracks in the abrasive or polishing tool.
Although the known abrasive elements have proven advantageous as they are easy to replace, they have been associated with certain disadvantages. They have not been so flexible as has been desirable since the mechanical deformation of the U profiles, produced from metal, might cause difficulties in adapting the abrasive elements to different types of tools and especially to tools of different diameters. Thus, it has been necessary to produce the abrasive elements for each particular tool.
The known abrasive elements have furthermore turned out to be disadvantageous in that they lose some of the bristles and/or lamellae after use for some time.
It is the object of the invention to provide a method for manufacturing a sweeper or abrasive element and to disclose the actual sweeper or abrasive element, which is not associated with the disadvantages of the known elements, and which is ready for use directly upon manufacture.
This is obtained according to the present invention by a method that is characterised in that a plastic profile is provided having a bottom and two legs projecting upward from it, which is manufactured in a compressed state so that the legs are elastically yielding pressed towards each other, so that the profile has a substantially triangular longitudinal cross-section in an initial state, and which is flexible in the longitudinal direction according to a plan perpendicular to the U bottom, that said profile is advanced, that the two U legs are spread, and that between them bristles are inserted between the two legs, or abrasive lamellae are inserted adjacent a first one of the two U legs and rigidifying bristles adjacent the second leg, that in the bottom of the U an adhesive member for gluing the bristles or the bristles and abrasive lamellae is inserted, that the U profile is brought back to its point of origin, the upper ends of the two legs approaching each other and thus squeezing the bristles or the lamellae and rigidifying bristles, and that the element formed is cut into desired lengths for use.
With this method it becomes possible to manufacture sweeper or abrasive elements such that the sweeper bristles or the rigidifying bristles and lamellae will not become loose during use. Thus, the adhesive member will ensure adhering of the bristles to the U profile. The profile may be manufactured in endless lengths by continuous conveyance of the U-shaped profile into which bristls and lamellae are inserted. After adherence and a deformation of the U profile have taken place, the latter may be cut into desired lengths without any risk that the outermost lamellae and bristles in the cut lengths of the abrasive element would fall out or become loose during use. Consequently, the U-shaped profile may be cut into any arbitrary length required for a given abrasive or polishing tool.
The U-shaped profile may easily be adapted to the tool and will also be able to be adapted to any diameter of the tool since the U-shaped profile is made flexible in the plane perpendicular to the bottom of the U.
A flexible U-shaped plastic profile is used in which the distance between the upper ends of the U legs in a non-deformed state is shorter than the distance between the lower ends of the U legs. This means in other words that a plastic profile is used in which the legs themselves have an elastic force towards each other in order to squeeze around the brushes and lamellae placed between the U legs. For this method it is preferred for the adhesive member to be a fusible plastic thread. Thus, it will be possible to deform both the U profile and the plastic thread during heating. Heating may take place thermally or by ultrasound. By the obtained plasticisation of the plastic it will be possible to embed the brushes and the lamellae in the plastic so that an integral unit results. This may be accomplished in a suitable manner by conducting the U profile with the brushes and lamellae arranged therein through a matrix. During a subsequent cooling the plastic profile may, by means of a suitably shaped matrix, be given a desired outer contour. This will frequently be a cross-section shape making it possible to place the abrasive element in a dovetailed or T-shaped track in the cylindrical surface of the abrasive tool.
When heating it is sufficient that at least a plasticisation of the thread is ensured. However, it will also be advantageous that at least partial plasticisation of the U profile bottom appears in order to establish an integral link of plastic from the inserted thread and plastic from the U profile.
In order to obtain an abrasive element ready for use, it is preferred, before cutting the abrasive element into desired lengths, to perform a separation of bristles and lamellae and a cut of the bristles into a length that is adapted to the length of the lamellae used.
In this manner an optimal relation between the bristles and lamellae is obtained so that a tool may be put to use as soon as the abrasive element has been inserted.
This takes place by separating bristles and abrasive lamellae, preferably by inserting a spreading member between the bristles and the lamellae so that they are conveyed in two parallel rows over a distance. In this manner cutting members may be applied to shorten the bristles so that they obtain a desired length. If desired, the abrasive lamellae may be shortened at the same time. However, this will rarely be the case since the abrasive lamellae are formed transversely of a sheet-shaped abrasive material, preferably emery cloth. By contrast, the bristles may have unequal lengths due to their being laid down.
The bristles are laid down by bristle threads being conveyed to the spread-out U profile with an orientation transversely of the U profile in such a manner that the centres of the bristles are situated approximately at the U profile. Then the centres of the bristles are pressed down into the U profile. This may take place simultaneously with laying down the adhesive member/the tread. Under this pressure the two bristle ends will project upward and will then have unequal lengths. Alternatively, the bristles may also be introduced with one end inserted into the U profile. Also in this case there will be an uncertainty as to the bristle length since the bristles may be displaced at a shorter or longer distance into the U profile.
It is preferred that during deformation the U profile is given a cross-section contour that has larger width at the bottom of the U profile. In this manner it is possible, as mentioned above, to place the profile in an undercut track. When the sweeper or the abrasive tool is rotating, the undercut track and the cross-section contour of the profile will then contribute to the appearance of a wedging effect so that the U legs are squeezed together and thus contribute to a secure retention of the sweeper bristles or the rigidifying bristles and lamellae in the element even if certain lamellae and/or bristles are not fully embedded or retained by the applied adhesive.
If an additional adhesive member is used between the U profile and the abrasive lamellae, a particularly secure retention of the abrasive lamellae may be established. Such additional adhesive member may either be placed on the lamellae before insertion into the U profile or during insertion into the U profile simultaneously with inserting the adhesive member first mentioned.
A sweeper or abrasive element according to the invention is characterised in that the profile is at least partially manufactured from plastic and is composed of a bottom and two legs projecting upward from it, said profile being flexible in the longitudinal direction according to a plan perpendicular to the U bottom, and wherein the legs are manufactured in a compressed state so that they are elastically yielding pressed towards each other, so that the profile has a substantially triangular longitudinal cross-section in an initial state, the distance between the upper ends of the U legs in a nondeformed state being shorter than the distance between the lower ends, and that the sweeper bristles or the abrasive lamellae and rigidifying bristles are retained in the U by an adhesive member in the form of plastic originating from a plastic thread between the sweeper and rigidifying bristles and from the inside of the profile, which have been heated above the plasticisation temperature so that the plastic encloses the sweeper bristles or the rigidifying bristles and abrasive lamellae and forms an integral unit.
Such a sweeper or abrasive element is advantageous because an integral unit is formed so that bristles and lamellae cannot become loose when the sweeper, abrasive or polishing tool is being used. The element is further advantageous because the plastic profile can be bent easily and consequently may be adapted to any diameter of the cylindrical surface of the sweeper, abrasive or polishing tool. Thus, the element may optionally be delivered to a user in endless lengths or cut into lengths fitting the tools of the individual user. Replacing the sweeper or abrasive element is performed easily and simply by inserting the formed U profile in an undercut track in the tool body. As the distance between the upper ends of the U legs is shorter than the distance between the lower ends, the abrasive element will, as explained above, be retained in the track.
The abrasive lamellae used will preferably be formed from an elongated abrasive cloth which is slit at one lateral edge. At the other lateral edge the lamellae are thus coherent at the part of the abrasive cloth that has not been slit. With this kind of abrasive cloth a mutual positioning of the abrasive lamellae in the abrasive element is obtained and at the same time handling the manufacture of the abrasive element is easier. Thus, the abrasive lamellae may be stored in a roll-shape and be unwound from such a roll and conveyed at a velocity corresponding to the conveyance velocity of the U-shaped profile and the adhesive member.